Detection circuit for sensing the input voltage of transformer

Abstract

A circuit for detecting an input voltage of a transformer is provided. The circuit includes a current source circuit coupled to a winding of a transformer. A current-to-voltage circuit is coupled to the current source circuit to generate a first voltage in response to a current outputted from the current source circuit. A sample-and-hold circuit generates an output voltage by sampling the first voltage. The transformer is coupled to the input voltage, and the output voltage is correlated to the input voltage of the transformer.

1. A detection circuit for detecting an input voltage, comprising:
 a current source circuit receiving a bias voltage and being coupled to an auxiliary winding of a transformer; 
 a current-to-voltage circuit, directly connected to the current source circuit to generate a first voltage in response to a current outputted from the current source circuit; and 
 a sample-and-hold circuit, generating an output voltage by sampling the first voltage, 
 wherein the transformer is coupled to an input voltage, the output voltage is correlated to the input voltage of the transformer, and the bias voltage is independent from the output voltage. 
 
   
   
     2. The detection circuit as claimed in  claim 1 , further comprising a pulse generator coupled to the sample-and-hold circuit to provide a pulse signal for the sample-and-hold circuit in response to a switching of the transformer. 
   
   
     3. The detection circuit as claimed in  claim 1 , further comprising a bias circuit coupled to the current source circuit to provide the bias voltage to the current source circuit. 
   
   
     4. The-detection circuit as claimed in  claim 1 , wherein the current source circuit is coupled to the auxiliary winding of the transformer through a resistor. 
   
   
     5. The detection circuit as claimed in  claim 1 , wherein the sample-and-hold circuit comprises a first capacitor to sample the first voltage. 
   
   
     6. A detection circuit, comprising:
 a current source circuit, coupled to a winding of a transformer; 
 a current-to-voltage circuit, coupled to the current source circuit to generate a first voltage in response to a current outputted from the current source circuit; and 
 a sample-and-hold circuit, comprising a first capacitor to sample the first voltage, a second capacitor to sample a signal from the first capacitor, and the capacitance of the second capacitor is larger than that of the first capacitor, generating an output voltage by sampling the first voltage, wherein the transformer is coupled to an input voltage, and the output voltage is correlated to the input voltage of the transformer.